Metal-oxide-semiconductor (MOS) devices are key components of modern integrated circuits. To satisfy the requirements of increasingly faster speed, the drive currents of MOS devices need to be increasingly greater. Since the drive currents of MOS devices are proportional to their gate widths, MOS devices with greater widths are preferred.
In addition, more functions need to be integrated into a single semiconductor chip, and hence more semiconductor devices need to be formed therein. Accordingly, semiconductor devices are required to be increasingly smaller, and device densities need to be increasingly higher. The requirements of smaller devices and higher drive currents cause the design of integrated circuits to be more and more complex. For example, high device density makes the overlay windows, which are allowable misalignment between different masks, to be small, and hence a small misalignment may cause a device failure.
The reduction in the overlay windows is further worsened by the introduction of Fin field-effect transistors (FinFET), which are widely used to increase drive currents. A FinFET includes a fin having a top surface and two sidewalls, and a gate over both the top surface and the sidewalls. Therefore, the FinFETs have increased effective gate widths since the sidewalls of the FinFETs are also used to conduct currents. However, FinFETs put an even higher requirement on the design of integrated circuits due to the process of forming and isolating fins. Particularly, FinFETs have small fins. It is thus difficult to align contacts accurately to the fins.
Additionally, conventional MOS device formation needs to form customized active regions and gate electrodes, and thus the pattern densities of the active regions, STI regions, and gate electrodes become an important issue for controlling device performance.
Accordingly, what are needed in the art are novel manufacturing methods and semiconductor device structures to simplify the design of integrated circuits.